Coinjection molding or multi-layer articles

ABSTRACT

A multi-cavity coinjection mold having a relatively large plurality of cavities for simultaneously molding a relatively large plurality of multi-layered articles including a) a plurality of cavity groups each defining a relatively small plurality of said cavities, a single balanced hot runner for supplying said relatively small plurality of cavities with contiguous different plastics materials, and a valve for sequentially supplying desired contiguous quantities of the plastics materials from plastics material sources, common to all of said groups, to the balanced hot runner; and b) a hot runner manifold system connected to the plastic material sources to supply the plastic materials to all of the valves; and related methods.

FIELD OF THE INVENTION

This invention relates generally to coinjection molding and particularlyrelates to an improved apparatus and method for simultaneously molding aplurality of multi-layered articles.

DEFINITIONS

As used herein:

"First and second materials" is intended to cover at least two materialswhich are sequentially supplied to an injection mold, it being entirelypossible that one or more other materials may be sequentially suppliedbefore, between, or after the first and second materials;

"Balanced Hot Runner" is a temperature controlled heated uninterruptedmaterial conveying system extending from a single input (e.g. a materialsource or metering valve) to a plurality of outputs (e.g. meteringvalves or injection mold cavities) comprising a single passage branchedinto a plurality of passages with each of said plurality of passages,communicating with one of the plurality of outputs, for conveyingmaterial therethrough to simultaneously supply equal quantities of thematerial to each of the outputs;

"Unbalanced Hot Runner" is a temperature controlled heated materialconveying system, for the passage of material from an input (e.g.material supply source) to a plurality of outputs (e.g. metering valvesfor metering the material for supply of metered quantities of thematerial to injection mold cavities), which is not branched to providepassages of identical cross-section and length and does not divide thesupplied material into equal quantities for the simultaneous supply ofthese quantities each to one of outputs.

BACKGROUND OF THE INVENTION

The manufacture of pure, or virgin, resin preforms for blow moldingcontainers is well known within the prior art. But since the advent ofrecycling, it is now possible to manufacture preforms with materialsthat are compositionally less pure than virgin materials. Such degraded,or recycled, materials not only yield positive environmental benefits inan ecologically fragile era but provide manufacturers with analternative manufacturing method which allows for substantial reductionsin costs.

But, since recycled materials are obtained from post consumer solidwaste, certain new manufacturing problems have been encountered thatwere heretofore previously unknown. For example, manufacturers must nowprovide, at increased costs, additional equipment for keeping the virginand recycled materials separate from each other. In addition,multi-layered articles, such as preforms, that are eventually used toform containers for food stuffs, have even further impediments by way ofrigid statutory guidelines. The guidelines, enacted by the Food and DrugAdministration (FDA), require that certain minimums must be met, orexceeded, before the containers can be approved as "qualified" tocontain food stuffs and before the foods are allowed to be distributedto the consumer population. One extremely noteworthy FDA provisionenacted theretowards provides for the assurance of product"cleanliness".

Currently, in order to meet the FDA cleanliness standards, a containermust be configured such that only surfaces of virgin materials contactthe foods and beverages therein. Other container surfaces, such as areasfor contacting the human mouth, e.g. the dispensing orifice on a sodacontainer, also require virgin material surfaces. As a result, it iseconomically desirable to provide manufacturers with a apparatus capableof utilizing recycled materials within containers while, at the sametime, preventing recycled materials from contacting the very foods andliquids that are to be distributed to, and consumed by, the public.

Some advances towards the aforementioned goal have been attained byusing coinjection molding techniques to manufacture multi-layeredcontainers. The multi-layered containers thence produced have interiorand exterior surfaces of the container comprised of virgin materialswhile the fill and support materials located within the interior of thecontainer walls comprise the degraded, less than pure, recycledmaterials. Consequently, the economies and conservation of utilizingrecycled materials is thereby achieved while simultaneously meeting thestrict FDA statutory requirements.

Prior art coinjection molding techniques that produce the multi-layeredcontainers described above, often first manufacture a multi-layeredpreform and then blow mold the preform into the final container. Theformation of multi-layered containers are described in detail, forexample, in Applicant's U.S. Pat. Nos. 4,550,043 and 5,221,507.

Typically, the preforms are injection molded in multi-cavity molds whichmay have as many as 96 cavities. These preforms are then simultaneouslyproduced by injecting appropriate amounts of a first and secondmaterial, i.e. virgin and recycled, into each of the cavities. To thisend, the mold defines a manifold arrangement to convey the two materialsto each of the singular cavities. Such an arrangement, as in Applicant'sprior patents, is known to convey each of the first and second materialscontiguously through a singular hot runner to the cavities. This allowsfor a reduction in equipment costs due to the singular hot runnerarrangement. The singular hot runner is repeatedly divided the materialsflowing therein into a plurality of flow paths for delivery to eachcavity and to thereby ultimately provide each cavity with asubstantially equal amount of metered material at substantially the sametemperature and at substantially the same time as every other cavity.Yet, with mold arrangements containing large numbers of cavities, suchas with forty-eight and ninety-six cavities, the two materialscontiguously flowing within a singular conduit have been known to haveinterface boundary problems between the virgin and recycled materialswhen conveyed contiguously over lengthy distances.

Other prior art multi-cavity mold apparatus, that use coinjectionmolding to form multi-layered preforms, utilize molds in which acompletely separate manifold system for each material, i.e. virgin andrecycled, is used to separately convey that specific material to thesingular cavities. The separate materials are then, either, injectedsimultaneously into the cavities using concentric nozzles or injectedsequentially into the cavities utilizing a valve arrangement closelyadjacent each cavity to control the flow from the separate manifolds.Such arrangements result in molds that are expensive and complex. Inaddition, such molds result in difficulties in controlling thetemperature of the material to be injected into the cavity in a mannersuch that each mold receives an accurately metered quantity of materialat substantially the same temperature.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anapparatus and method that yields a delivery method for a first andsecond material that delivers the respective materials at substantiallythe same temperature and at reduced costs due while conveyingsubstantially equivalent amounts of the respective materials atsubstantially simultaneous delivery times.

It is a further object of the present invention to provide a moredistinct division between the recycled and pure materials beingcontiguously conveyed within the same conduit to the individual moldcavities in order to more accurately provide a substantially equivalentamount of molding materials to each cavity.

It is a further object of the present invention to provide a method andapparatus using a multi-cavity coinjection mold which avoids the complexconstruction and expense of prior art multi-cavity coinjection molds andwhich provides a low cost, relatively simple, easy to regulate moldwhich is suitable for use on existing machinery at minimal conversioncosts.

According to the invention, these and other objects are achieved byproviding an apparatus and method that utilizes a hot runner manifoldsystem which keeps at least one of a plurality of molding materials,virgin and recycled, for example, physically separated from the other(s)until they have been conveyed to a plurality of cavity groups eachcomprising a plurality of individual mold cavities. Once conveyed to thegroups, the molding materials are combined by a timed valve distributionmechanism, one valve mechanism per group, to produce a supply ofmaterial comprised of metered contiguous quantities of the differentmaterials. The contiguous quantities of material are then conveyed,within each group, in a balanced hot runner system wherein the materialis evenly divided for injection simultaneously and sequentially into theindividual cavities in desired amounts of the materials to produce aplurality of similar multi-cavity preforms.

According to the invention there is provided a multi-cavity coinjectionmold having a relatively large plurality of cavities for simultaneouslymolding a corresponding relatively large plurality of multi-layeredarticles comprising: a) a plurality of cavity groups each defining (i) arelatively small plurality of said cavities, (ii) a single balanced hotrunner for sequentially supplying said relatively small plurality ofcavities with contiguous different plastics materials, each plasticsmaterial being supplied simultaneously in substantially equal quantitiesto each of said relatively small plurality of cavities, (iii)temperature control means for maintaining said balanced hot runner andsaid cavities at desired temperatures; and (iv) valve means forsequentially supplying desired contiguous quantities of said plasticsmaterials from of said plastics materials, common to all of said groups,to said balanced hot runner for contiguous sequential passage of saidplastic materials to each said small plurality of cavities; and b) hotrunner means connected to the plastics material sources respectively tosupply the plastics materials to all said valve means.

Also according to the invention there is provided a coinjection methodfor multi-layer coinjection mold having a relatively large plurality ofcavities for simultaneously molding a corresponding relatively largeplurality of multi-layered articles comprising the steps of: a) dividingthe relatively large plurality of cavities into a plurality of cavitygroups each defining a relatively small plurality of said cavities; b)providing a single balanced hot runner for each group; c) temperaturecontrolling said balanced hot runners and said cavities at desiredtemperatures; d) providing a valve means for each group, for controllingthe sequentially supply of desired contiguous quantities of saidplastics materials from sources of said plastics materials, common toall of said groups, to the balanced hot runner of its associated groupfor contiguous sequential passage of said plastics materials to eachsaid small plurality of cavities of that group; and e) sequentiallysupplying each said cavity with contiguous different plastics materialssimultaneously in substantially equal quantities by way of said balancedhot runners.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross-section of a portion of amulti-sequential coinjection mold system according to the presentinvention;

FIG. 2 is a fragmentary diagrammatic view of a multi-cavity coinjectionmold according to a first embodiment of the present invention;

FIG. 3 is a diagrammatic view of one valve and nozzle arrangement of thepresent invention;

FIG. 4 is a fragmentary diagrammatic view of a multi-cavity coinjectionmold according to a second embodiment of the present invention; and

FIG. 5 is a block diagram illustration of a third embodiment of amulti-cavity coinjection mold according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a cavity group 1 of a larger multi-cavity moldfor the sequential coinjection molding of multi-layered preforms for theblow molding of multi-layered containers comprising interior andexterior surfaces of a virgin material (e.g. polyethylene terephthalate,PET) is illustrated as having four cavities 3 therein. It will beappreciated by those skilled in the art that, in practice, the cavitygroup 1 depicted is part of a multi-cavity coinjection mold that mayhave forty-eight, sixty-four, ninety-six or even more cavities. Fourcavities are used in this example to simplify explanation of the presentinvention which is applicable to molds with cavity groups 1 having twoor more cavities, particularly where the number of cavities is amultiple of two.

Each cavity is defined by a core rod 5 and a female cavity portion 7,formed in the mold itself, together with a neck defining split neck ring9 through which the core pin 5 extends to a core pin/split neck ringsupport block 11 through which core pin cooling water may be supplied byway of cooling water tubes 13. At the base 15 of each cavity is a gate17 through which passes the material which will form the preform in thatcavity.

The cavity groups 1 together form the multi-cavity mold. The cavitygroups 1 are substantially identical and only one will be described indetail. The exemplary cavity group defines a balanced hot runnerillustrated generally by reference number 19 which extends from divertervalves 21 and 23 which regulate the supply of virgin and recycled moltenPET from plasticizer barrels 25 and 27, respectively, under the controlof material metering ram pots 29 and 31. The diverter valves 21 and 23regulate the supply of molten PET to a single balanced hot runner 33forming part of the manifold system 19. The balanced hot runner 33 isdivided into two hot runners 35 of identical cross-section and lengthand these hot runners 35 are again divided each into further hot runners37, again of identical cross-section and length, which lead one to eachcavity 3 by way of its associated gate 17, thereby to ensure that themolten PET is metered in substantially equal amounts simultaneously toeach cavity. Heating means 39 is provided to maintain and control thetemperature of the molten PET as it is distributed through the hotrunners of the manifold system. To facilitate accurate temperaturecontrol the manifold system is insulated by insulating means 41.

Construction details of the mold 1, its manifold system, the heatingmeans and the insulating means together with the cavity design andcooling arrangements for the core pins and cavities, the split neckrings etc. are considered to be conventional in this technology and willbe readily apparent to those skilled in the art. Similarly theplasticizer barrels and ram pots are of conventional construction as arethe general engineering details of the diverter valves. Accordinglythese matters will not be described in detail in this application.

The diverter valves 21, 23 provides contiguous materials within singularconduit 33 as a continuous supply. Such contiguous length of material issupplied to singular conduit 33 from diverter valves 21, 23 whichregulate the supply of the first and second materials from a temperaturecontrolled hot runner manifold system 50.

In operation, hot runner system 50 receives first and second materialsfrom plasticizer barrels 25 and 27 under control of metering ram pots 29and 31, respectively. Such hot runner system 50 then separately conveysthe first and second materials to each of the appropriate cavity groups1 (indicated in FIG. 1 by the jagged break of hot runner manifold system50) for the purpose ultimately of injecting each of the four individualcavities 3 within each region with appropriate amounts of material. Hotrunner system 50 conveys first and second materials, through respectiveunbalanced hot runners 52 and 54, to one valve distribution mechanism21, 23 per cavity group 1.

It should be appreciated that separate conveyance of the first andsecond materials to regions proximate the cavities will prevent anyinterface boundary difficulties between the first and second materialssince the two materials are not within a singular conduit. Once combinedwithin the singular conduit 33, the distances traveled by the contiguousfirst and second materials is minimal and the difficulties of lengthycontiguous travel are minimized. Simultaneously, equipment costadvantages are realized since the hot runner manifold system 30 is onesingular system for both materials. In addition, hot runner manifoldsystem 50 need not be a balanced conveyance system.

With reference to hot runner manifold system 50, it will be appreciatedby those skilled in the art that separate and distinct conduits 52 and54 may be used to convey materials from respective plasticizers 25 and27 having substantially different processing temperatures. In suchcircumstances, the heating means 42 and insulating materials 43 wouldalso be separate and distinct for each conduit 52 and 54. If thematerials are of the same processing temperature, the temperaturecontrol means 42 may be either the same unit or adjusted to theequivalent temperatures. In either event, the conveyance of the specificmaterials are again kept separate until conveyed to the appropriatecavity groups 1. Conveyed first and second materials are then likewisesupplied to one timed valve distribution system 21, 23 per group, forcombining the materials into a contiguous length, and supplied to abalanced hot system 19, nozzle 28 and eventually to the appropriateindividual cavity 3.

With reference to FIG. 2, an embodiment of a multi-cavity coinjectionmold in accordance with the present invention will now be described.Only a portion of the mold is illustrated in FIG. 2 for purposes ofsimplicity. The mold has a large plurality of cavities 3, for example24, 48 or 96, and these cavities are divided evenly into a plurality ofcavity groups 1 in the present embodiment, each consisting of four (4)cavities 3, an associated balanced hot runner 33 and diverter valve 44,all of which function and are substantially as described with referenceto FIG. 1. Although illustrated with each cavity group consisting offour (4) cavities and their associated components, it will beappreciated that each cavity group is formed of a relatively smallnumber of cavities, for example 2, 3, or 4, the total number of cavitiesof the mold being evenly divisible by the number of cavities in eachcavity group.

A hot runner manifold system 50 delivers separate molding materials fromplasticizers 25 and 27 with their associated ram ports 29 and 31 throughseparate manifolds 52 and 54 for delivery to the diverter valves of eachcavity group 1. The diverter valves 44 of the cavity groups arepreferably synchronously operated to provide for the simultaneousinjection of contiguously flowing materials in the manifolds 33 for thesimultaneous injection of those materials with equal quantities to allof the cavities of the mold. The diverter valves 44 may be synchronouslyoperated by electronic control or by a mechanical interconnectionbetween all of the diverter valves or sets of the diverter valves, forexample by a control shaft 45 shown diagrammatically in FIG. 2. Asdiscussed elsewhere, the manifolds 52 and 54 may be separatelydimensioned, do not need to be of a balanced manifold form and may beseparately temperature controlled to provide different viscosities ofmaterials to be injected into the cavities as control processing mayrequire.

Now referring to FIG. 3, a diverter valve variant 45 is illustrated. InFIG. 3, the cavity group includes only two (2) cavities 3 supplied withcontiguous materials for the coinjection of articles in the cavities byway of a balanced hot runner 33 which doubles as the nozzle arrangementfor each of the cavities by virtue of a reduction in the cross-sectionalarea of the manifold system closely adjacent the valve whereby thenozzles extend substantially all the way from the valve to each of thecavities 3. The valve rotates about axis 51 under the control of acontrol mechanism to receive materials from manifold extensions of themanifolds 52 and 54. Thus it will be appreciated that although there isa requirement for a hot runner balanced manifold for the contiguoussupply of materials from the diverter valves 45 to the cavities, a partof that balanced manifold or substantially all of that balanced manifoldmay also constitute an extended nozzle terminating at the gate of eachof the cavities.

It is also possible that the multi-layered article formed may bemanufactured from three or more materials sequentially injectedsubstantially simultaneously at the respective cavities. Such anembodiment could consist of a third conveyance means within hot runnermanifold system 50 and appropriate revisions to valve mechanism 21, 23or 45 or to the use of arrangements such as illustrated in FIGS. 4 and 5hereof.

The second embodiment illustrated in FIG. 4 comprises multi-cavitycoinjection mold having four cavity groups 1. The mold could have andusually would have a larger plurality of cavities 3, for example 24, 48or 96, and these cavities would be divided evenly into a plurality ofthe cavity groups 1, each consisting of four (4) cavities 3, anassociated balanced hot runner 33 and diverter valve 44, all of whichfunction and are substantially as described with reference to FIG. 1.Although the illustrated with each cavity group consisting of four (4)cavities and their associated components, it will be appreciated thateach cavity group may be formed of a relatively small number ofcavities, for example 2, 3, or 4, the total number of cavities of themold being evenly divisible by the number of cavities in each cavitygroup.

A hot runner manifold system 58 delivers separate molding materials fromplasticizers 25, 27 and 60 with their associated ram pots 29, 31 and 62through separate runners 52 and 64 for delivery to the diverter valves44 of each cavity group 1. As with the first embodiment, the divertervalves 44 are preferably synchronously operated.

In this second embodiment the three plasticizers may provide threedifferent materials, for example, virgin PET form plasticizer 60,recycled PET from plasticizer 25 and another material, such as a barriermaterial, from plasticizer 27. Alternatively plasticizer 27 could alsosupply virgin PET. In either circumstance the virgin PET fromplasticizer 60 is supplied separately by way of an unbalanced hot runner66 to the diverter valves 44 while the materials from the plasticizers25 and 27 are metered by a diverter valve 68 to a balanced hot runner 64for contiguous flow therethrough to supply the materials simultaneouslyand sequentially in equal quantities to the diverter valves 44 formetering, with the virgin PET from the unbalanced hot runner 66, toprovide the contiguous supply of the three materials through the balancehot runners 33. Operation of the diverter valves 44 to ensureappropriate material metering.

In the event the material from the plasticizers 27 and 60 both beingvirgin PET, the arrangement of FIG. 4 can advantageously be used tosupply virgin PET from plasticizer 60 to diverter valves 44 without anypossible contamination by the recycled PET, thereby to facilitate theformation of the inner surface of a multi-layer article molded in thecavities with sufficiently pure virgin material for the prolongedexposure of beverages or food stuffs to that inner surface without fearof contamination. This is so, even though the materials passcontiguously through the balanced hot runners 33, as a result of theabbreviated form of runner 33 compared with the arrangementscontemplated in applicants aforementioned patents.

In the variation of the second embodiment illustrated as a thirdembodiment in FIG. 5 four plasticizers 70, 72, 74 and 76 which may haveassociated ram pots (not shown in FIG. 5) separately supply a pluralityof up to four different materials to diverter valves 78 and 80 formetering to balanced hot runners 82 and 84 for the contiguous supply ofmaterials from plasticizers 70, 76 and 72, 74, respectively, to thediverter valves 44, of cavity groups 1, for metering thereby for thecontiguous supply thereof through the balanced hot runners of the cavitygroups to the cavities thereof in a manner substantially as previouslydescribed herein. As mentioned materials from different plasticizerscould be the same.

It will be appreciated that in, for example, the second embodiment asingle plasticizer could be used to supply the same material to both theunbalanced hot runner 58 and the diverter valve 68 and that similarvariations are possible in the third embodiment. In addition thebalanced hot runners 82, 84 may be identical in order to balance thecontiguous supply of metered material therethrough or may be differentfrom each other and/or controlled at different temperatures to providedesired characteristics of material flow to the cavities.

The valve mechanisms may be provided with an "off" or closed position aswell as a position for the introduction of each material sequentiallyand contiguously into the manifold 33.

Of course it will be appreciated that diverter valve operation could beadjusted, if injection molding in different cavity groups is unbalancedthereby causing non-uniform layers and or parts from cavity group tocavity group, by sequentially operating the valves and/or changing valvetiming to adjust material flow from one cavity group to another, forexample, so that cavity groups that would receive the most materialwould have their diverter valve operation delayed to compensate andbalance the flow of material to the groups.

One of the material may be recycled PET or a barrier material e.g.ethylene vinyl alcohol (EVOH) disposed intermediate polyester layers ofthe article.

What is claimed is:
 1. A multi-cavity coinjection mold having a largeplurality of cavities for simultaneously molding a corresponding largeplurality of multi-layered articles comprising:a) a plurality of cavitygroups making up the large plurality of cavities, said cavity groupseach made up of (i) a small plurality of said cavities, (ii) a singlebalanced hot runner for sequentially supplying said small plurality ofcavities with contiguous different plastics materials, each plasticsmaterial being supplied simultaneously in substantially equal quantitiesto each of said small plurality of cavities, (iii) temperature controlmeans for maintaining said balanced hot runner and said cavities atdesired temperatures; and (iv) valve means for sequentially supplyingdesired contiguous quantities of said plastics materials from plasticsmaterials sources, common to all of said groups, to said balanced hotrunner for contiguous sequential passage of said plastic materials toeach said small plurality of cavities; b) hot runner means connected tothe plastics material sources respectively to supply the plasticsmaterials to all said valve means; and c) wherein the hot runner meanscomprises a balanced hot runner for supplying contiguously meteredquantities of different said plastics materials received from saidplastics sources, by way of the valve means, simultaneously insubstantially equal quantities to each said small plurality of cavities.2. A multi-cavity coinjection mold according to claim 1 wherein allcavity groups have the same number of cavities and said single balancedhot runners of all cavity groups are identical in cross-sectionalconfiguration and length thereby to facilitate said simultaneoussequential supply of said plastics materials to said large plurality ofcavities.
 3. A multi-cavity coinjection mold according to claim 2wherein each single balanced hot runner is evenly divided a plurality oftimes to form a sequence of hot runners terminating in a single runnerto each said cavity.
 4. A multi-cavity coinjection mold according toclaim 1 wherein each said balanced hot runner is insulated and saidtemperature control means maintains the plastics materials in each saidbalanced hot runner at a desired temperature.
 5. A multi-cavitycoinjection mold according to claim 1 wherein the small plurality ofcavities is one of two, three and four in number.
 6. A multi-cavitycoinjection mold according to claim 5 wherein the small plurality isfour in number.
 7. A multi-cavity coinjection mold according to claim 1wherein said balanced hot runner of each cavity group supplies eachcavity of that group by way of a nozzle leading to a gate of thatcavity.
 8. A multi-cavity coinjection mold according to claim 7 whereinthe nozzle of each cavity leads to its associated gate by a passagedefining part of the associated balanced hot runner.
 9. A multi-cavitycoinjection mold according to claim 8 wherein the nozzles of each cavitygroup are adjacent their associated valve means.
 10. A multi-cavitycoinjection mold according to claim 1 wherein operation of the valvemeans of the groups is synchronized.
 11. A multi-cavity coinjection moldaccording to claim 1 wherein the valve means each have at least threeoperating states, i) namely, to supply a first plastic material, ii) tosupply a second plastics material, and iii) an off position.
 12. Amulti-cavity coinjection mold according to claim 1 wherein the hotrunner means comprises a plurality of separate hot runners, at least oneof which is unbalanced, for separately supplying different said plasticsmaterials separately to all said valve means.
 13. A multi-cavitycoinjection mold according to claim 12 wherein the different plasticsmaterials consist of a first and second materials and the hot runnermeans comprises two unbalanced hot runners, one for each of the firstand second materials.
 14. A multi-cavity coinjection mold having a largeplurality of cavities for simultaneously molding a corresponding largeplurality of multi-layered articles comprising:a) a plurality of cavitygroups making up the large plurality of cavities, said cavity groupseach made up of (i) a small plurality of said cavities, (ii) a singlebalanced hot runner for sequentially supplying said small plurality ofcavities with contiguous different plastics materials, each plasticsmaterial being supplied simultaneously in substantially equal quantitiesto each of said small plurality of cavities, (iii) temperature controlmeans for maintaining said balanced hot runner and said cavities atdesired temperatures; and (iv) valve means for sequentially supplyingdesired contiguous quantities of said plastics materials from plasticsmaterials sources, common to all of said groups, to said balanced hotrunner for contiguous sequential passage of said plastic materials toeach said small plurality of cavities; b) hot runner means connected tothe plastics material sources respectively to supply the plasticsmaterials to all said valve means, wherein the hot runner meanscomprises a plurality of separate hot runners, at least one of which isunbalanced, for separately supplying different said plastics materialsseparately to all said valve means; and c) wherein the hot runner meansalso comprises a balanced hot runner for supplying contiguously meteredquantities of different said plastics materials received from saidplastics sources, by way of the valve means, simultaneously insubstantially equal quantities to each said small plurality of cavities.15. A multi-cavity coinjection mold having a large plurality of cavitiesfor simultaneously molding a corresponding large plurality ofmulti-layered articles comprising:a) a plurality of cavity groups makingup the large plurality of cavities, said cavity groups each made up of(i) a small plurality of said cavities, (ii) a single balanced hotrunner for sequentially supplying said small plurality of cavities withcontiguous different plastics materials, each plastics material beingsupplied simultaneously in substantially equal quantities to each ofsaid small plurality of cavities, (iii) temperature control means formaintaining said balanced hot runner and said cavities at desiredtemperatures; and (iv) valve means for sequentially supplying desiredcontiguous quantities of said plastics materials from plastics materialssources, common to all of said groups, to said balanced hot runner forcontiguous sequential passage of said plastic materials to each saidsmall plurality of cavities; b) hot runner means connected to theplastics material sources respectively to supply the plastics materialsto all said valve means; and c) wherein the hot runner means comprisesat least two balanced hot runners each for supplying contiguous meteredquantities of different said plastics materials received from saidplastics sources, by way of the valve means, simultaneously insubstantially equal quantities to each said small plurality of cavities.